土地利用历史及管理对内蒙古典型草原群落结构的影响

在内蒙古典型草原农牧交错区多伦县境内，进行了土地利用历史和管理对群落结构演变影响的研究。探讨了模拟降雨和添加N、P对草地群落结构的单因子效应和互作效应。土地利用历史选择了围封禁牧和弃耕两种。弃耕地的弃耕历史为4年，围封禁牧分别为围封1年和围封4年。研究在2005年进行了一年，主要研究结果如下： 1. 在内蒙古典型草原地区，土地利用历史对物种丰富度、植被盖度的影响不大，但对物种分布均度、植被高度影响显著。弃耕地的物种分布均质性较差，但植被高度高于围封草地。弃耕地的物种多样性指数、枯落物覆盖度低于围封草地，围封草地中围封4年的又低于围封1年。 2. 增雨对内蒙古典型草原群落的物种丰富度无显著影响，但利于植被盖度和植被高度的增加。增雨也使得群落的枯落物覆盖度和空地覆盖比例下降。在获得水分的条件下豆科植物的扩张速度快于禾本科植物，表现出了群落结构分异的趋势。 3. 添加N素和P素没有引起群落物种丰富度的明显变化，但添加N素利于物种数目增加。添加N素还使得草地植被盖度增加、枯落物覆盖度和空地覆盖比例下降，但添加P素没有产生类似的效果。添加5g/m2 以上的N就会引起内蒙古典型草原枯落物覆盖度的显著降低。添加N素后，禾本科植物盖度增加，但豆科植物响应不强烈;添加P素后，豆科植物盖度增势明显。因此，豆科植物对P素反应敏感，而对N素渴求不强烈。 4. 水、N、P交互对物种丰富度和植被高度影响都不大，但都有促使植被盖度增加、枯落物覆盖度和空地覆盖比例下降的趋势。水、N、P交互还使得禾本科盖度增加，但除水、P交互外，各交互组合对豆科植物盖度的影响都不大明显。 综上所述，土地利用方式和管理是内蒙古典型草原群落结构演变的重要驱动力。在当今人类活动日益加剧的形势下，天然植被受人为的干扰越来越大。如何保护内蒙古典型草原的植被，是许多研究者共同肩负的重任。

STUDY ON THE SPATIAL PATTERNS OF LAND-USE CHANGE AND ANALYSES OF DRIVING FORCES IN NORTHEASTERN CHINA DURING 1990-2000

Land-use change is an important aspect of global environment change. It is, in a sense, the direct result of human activities influencing our physical environment. Supported by the dynamic serving system of national resources, including both the environment database and GIS technology, this paper analyzed the land-use change in northeastern China in the past ten years (1990 - 2000). It divides northeastern China into five land-use zones based on the dynamic degree (DD) of land-use: woodland/grassland - arable land conversion zone, dry land - paddy field conversion zone, urban expansion zone, interlocked zone of farming and pasturing, and reclamation and abandoned zone. In the past ten years, land-use change of northeastern China can be generalized as follows: increase of cropland area was obvious, paddy field and dry land increased by 74. 9 and 276. 0 thousand ha respectively; urban area expanded rapidly, area of town and rural residence increased by 76. 8 thousand ha; area of forest and grassland decreased sharply with the amount of 1399. 0 and 1521. 3 thousand ha respectively; area of water body and unused land increased by 148. 4 and 513. 9 thousand ha respectively. Besides a comprehensive analysis of the spatial patterns of land use, this paper also discusses the driving forces in each land-use dynamic zones. The study shows that some key biophysical factors affect conspicuously the conversion of different land- use types. In this paper, the relationships between land- use conversion and DEM, accnmlated temperature(>= 10 degrees C) and precipitation were analysed and represented. We conclude that the land- use changes in northeast China resulted from the change of macro social and economic factors and local physical elements. Rapid population growth and management changes, in some sense, can explain the shaping of woodland/grassland - cropland conversion zone. The conversion from dry land to paddy field in the dry land - paddy field conversion zone, apart from the physical elements change promoting the expansion of paddy field, results from two reasons: one is that the implementation of market-economy in China has given farmers the right to decide what they plant and how they plant their crops, the other factor is originated partially from the change of dietary habit with the social and economic development. The conversion from paddy field to dry land is caused primarily by the shortfall of irrigation water, which in turn is caused by poor water allocation managed by local governments. The shaping of the reclamation and abandoned zone is partially due to the lack of environment protection consciousness among pioneer settlers. The reason for the conversion from grassland to cropland is the relatively higher profits of fanning than that of pasturing in the interlocked zone of farming and pasturing. In northeastern China, the rapid expansion of built-up areas results from two factors: the first is its small number of towns; the second comes from the huge potential for expansion of existing towns and cities. It is noticeable that urban expansion in the northeastern China is characterized by gentle topographic relief and low population density. Physiognomy, transportation and economy exert great influences on the urban expansion.